A memory system provided with non-volatile memory has a backup power source, such as a battery or a capacitor, for an invalid interruption of electric power supply. When detecting the invalid interruption of electric power supply, the memory system switches the power source to the backup power source from an external power source, and saves necessary data to the non-volatile memory from volatile memory within the period of supplying electric power by the backup power source in order to protect the data from being lost.
During the data saving operation, the non-volatile memory stores a progress log indicating the progress of the data save in order that the progress log is used for data recovery or failure analysis upon the data save.
Electric power exceeding the capacity of the backup power source cannot be consumed upon non-volatilization of the data and the progress log. Therefore, it is necessary to reduce the power consumption as much as possible to extend the backup time of the power source.